1. Field of the Invention
This invention relates to a field conversion system for rigid endoscopes which are used in the fields of medicine and industry and are inserted into cavities inside a human body and a pipe so that an object part can be observed by an external display.
2. Description of Related Art
As an example of a surgical operation, a method is known that a rigid endoscope is inserted into a human body to display an affected part on the image screen of a TV monitor or the like, and an operator manipulates, by remote control, various treatment tools, such as a suture instrument, electric knife, and cavitron ultrasonic surgical aspirator, inserted into the human body independently of the endoscope, while observing the image screen to treat the affected part. Where such methods are applied to various treatments, It is desirable that the affected part to be treated is displayed at a nearly middle position of the monitor screen and with the size of an image the operator desires. Thus, in order to enable the operator to devote himself exclusively to the treatment, a scope holding assistant has been adopted in addition to the operator. The scope holding assistant has manipulated the rigid endoscope in response to the oral instructions of the operator to adjust the direction and position of the rigid endoscope being inserted and to control the movement of a visual field and the size of the image.
In this case, however, there are problems that a full-time scope holding assistant must be adopted and that because a cooperation between the operator and the assistant Is difficult, work efficiency is impaired and the operator may be irritated according to circumstances. Thus, in order to solve these problems, field conversion systems for rigid endoscopes using conventional, optical trimming techniques are proposed by Japanese Patent Preliminary Publication Nos. Hei 8-332169 and Hei 9-28663. According to these publications, it becomes possible that the operator carries out a field conversion by himself without virtually affecting the manipulation of the treatment tools.
Each of the above publications, however, fails to disclose specific means for solving the following three problems encountered when the field conversion is made. The first problem refers to optical interchangeability with an existing observation system for rigid endoscopes. The observation system for rigid endoscopes which already has widespread use is designed so that the rigid endoscope is provided to be independent of an imaging device and a combination of both can be arbitrarily changed to make observations. However, where the change of this combination is made possible, each of the publications does not set forth the arrangement of an optical system capable of effectively performing the function of the field conversion.
The second problem refers to the relationship of performance between a rigid endoscope and an image sensor. In order to make a magnified image observable with good image quality, it is necessary to use a rigid endoscope of high image quality having the amount of information several times that of the image sensor. In this case, the amount of information which can be transmitted in a wide-angle condition is restricted by that of the image sensor. Thus, if an image sensor with a small amount of information is used, the performance of the rigid endoscope of high image quality will not be optimized. Each of the above publications fails to set forth means for overcoming this difficulty.
The third problem relates to a stereoscopic observation. Recently, with the advent of a rigid endoscope for stereoscopy, the remote control of treatment tools with stereoscopy has been intended. Each publication, however, does not disclose a specific construction such that the field conversion and the stereoscopy are compatible with each other.